This invention relates to a catalyst component and a catalyst system which is useful for the stereoregular polymerization or copolymerization of alpha-olefins and more particularly concerns a magnesium-containing supported titanium-containing catalyst component which contains an advantageous modifier system.
Use of solid, transition metal-based, olefin polymerization catalyst components is well known in the art including such solid components supported on a metal oxide, halide or other salt such as widely-described magnesium-containing, titanium halide-based catalyst components. Such catalyst components are referred to as "supported." Although many polymerization and copolymerization processes and catalyst systems have been described for polymerizing or copolymerizing alpha-olefins, it is advantageous to tailor a process and catalyst system to obtain a specific set of properties of a resulting polymer or copolymer product. For example, in certain applications, a combination of high activity, stereospecificity are required together with polymer characteristics such as good morphology, desired particle size distribution, acceptable bulk density and the like.
Typically, supported catalyst components useful for polymerizing propylene and higher olefins as well as for polymerizing propylene and higher olefins with a minor amount of ethylene contain an electron donor component as an internal modifier. Such internal modifier is an integral part of the solid supported component as is distinguished from an external electron donor component, which together with an aluminum alkyl component, comprises the catalyst system. Typically, the external modifier and aluminum alkyl are combined with the solid supported component shortly before the combination is contacted with an olefin monomer.
Selection of the internal modifier can affect catalyst performance and the resulting polymer formed from a catalyst system. As stated above, it is advantageous and an advance in the art to discover internal modifiers including combinations of modifiers which, when incorporated into a supported catalyst, produce-desired effects on the polymerization process and the polymer produced.
Generally, organic electron donors have been described as useful in preparation of the stereospecific supported catalyst components including organic compounds containing oxygen, nitrogen, sulfur, and/or phosphorus. Such compounds include organic acids, organic acid anhydrides, organic acid esters, alcohols, ethers, aldehydes, ketones, amines, amine oxides, amides, thiols, various phosphorus acid esters and amides, and the like. Mixtures of organic electron donors have been described as useful in incorporating into supported catalyst components.
Examples of organic electron donors are described in commonly assigned U.S. Ser. No. 07/731,499, filed Jul. 17, 1991, incorporated by reference herein. Other examples of other electron donor systems include those described in U.S. Pat. Nos. 4,971,937, 5,068,213, 5,095,153, and 5,106,807, as well as published European application EP 0 452 156. These references generally describe classes of diethers useful as electron donor components. Other electron donors are described in U.S. Pat. Nos. 3,642,746, 4,186,107, 4,473,660, 4,522,930, 4,565,798, 4,693,990, 4,814,312, 4,829,034, and 4,904,628.
Numerous individual processes or process steps have been disclosed to produce improved supported, magnesium-containing, titanium-containing, electron donor-containing olefin polymerization or copolymerization catalysts. For example, Arzoumanidis et al., U.S. Pat. No. 4,866,022, incorporated by reference herein, discloses a method for forming an advantageous alpha-olefin polymerization or copolymerization catalyst or catalyst component which involves a specific sequence of specific individual process steps such that the resulting catalyst or catalyst component has exceptionally high activity and stereospecificity combined with very good morphology. A solid hydrocarbon-insoluble, alpha-olefin polymerization or copolymerization catalyst or catalyst component with superior activity, stereospecificity and morphology characteristics is disclosed as comprising the product formed by 1) forming a solution of a magnesium-containing species from a magnesium hydrocarbyl carbonate or magnesium carboxylate; 2) precipitating solid particles from such magnesium-containing solution by treatment with a transition metal halide and an organosilane; 3) reprecipitating such solid particles from a mixture containing a cyclic ether; and 4) treating the reprecipitated particles with a transition metal compound and an electron donor.
Arzoumanidis et al., U.S. Pat. No. 4,540,679, incorporated by reference herein, discloses a process for the preparation of a magnesium hydrocarbyl carbonate by reacting a suspension of a magnesium alcoholate in an alcohol with carbon dioxide and reacting the magnesium hydrocarbyl carbonate with a transition metal component.
Arzoumanidis et al., U.S. Pat. No. 4,612,299, incorporated by reference herein, discloses a process for the preparation of a magnesium carboxylate by reacting a solution of a hydrocarbyl magnesium compound with carbon dioxide to precipitate a magnesium carboxylate and reacting the magnesium carboxylate with a transition metal component.
In addition, polymer or copolymer morphology often is critical and typically depends upon catalyst morphology. Good polymer morphology generally involves uniformity of particle size and shape, resistance to attrition and an acceptably high bulk density. Minimization of very small particles (fines) typically is very important especially in gas-phase polymerizations or copolymerizations in order to avoid transfer or recycle line pluggage. Therefore, it is highly desirable to develop alpha-olefin polymerization and copolymerization catalysts and catalyst components that have good morphology, and in particular, a narrow particle size distribution. Another property which is important commercially is the maintenance of an acceptably high bulk density.